Photovoltaic power plants employ solar cells to convert solar radiation to electrical energy. Photovoltaic power plants also include photovoltaic inverters (“inverters”), which convert direct current (DC) generated by the solar cells to alternating current (AC) suitable for delivery to a point of interconnect (POI) with a utility grid through a network of transformers and transmission lines.
The role of inverters in supporting grid integration requirements in the context of large photovoltaic power plants is still evolving. While utility grade inverters, due to their topology and controllability, offer extended capabilities, such as controlled reactive power delivery, frequency-power droop control, and fault-ride-through, practical challenges associated with coordinated control of multiple inverters operating in parallel in a large photovoltaic power plant have not been fully explored or understood. Inverters are highly flexible and controllable devices, but they are only capable of responding to conditions present at their terminals. In addition, a large photovoltaic plant contains multiple, distributed inverter stations, typically with non-identical circuit impedances and dynamic characteristics. As the inverters used in a large photovoltaic power plant may be procured from multiple vendors, several of their key parameters, such as active and reactive power ratings, output over-voltage tolerance, and control response rates, may be highly diverse between inverter stations. The distances of the inverters to the POI with the utility grid and the limitations in sensing of signals at the POI impose additional constraints on the communication infrastructure and on the achievable control response rates.